Over the years, the radio frequency identification technologies, commonly called RFID, have had a wide spread becoming the basic resource for tracking operations in many areas, including: logistics, security, controls, monitoring of things and people, etc. The acronym RFID (Radio Frequency Identification) refers to a technology for the identification and/or automatic storage of information relating to objects, animals or people, based on the ability to store data by specific electronic “labels”, called “Tags” (or transponders), and on the their ability to reply to the remote interrogation by means of special fixed or portable equipment, called “readers” (or interrogators). This identification is made using radio frequency signals, which permit to communicate with such tags.
Attaching an RFID Tag to the objects subject to monitoring allows to uniquely identify them or possibly adding useful information, suitably stored in the Tag itself. Compared to previous technologies, an RFID element doesn't need to be in contact to be read, as it happens with magnetic strips, and, moreover, may not even be directly visible to be read, as it happens, instead, for barcodes. These characteristics have led to an exponential growth in the number and type of RFID carrying objects on the market and aroused the interest to develop further applications and to increase their functionality. A typical problem that has arisen is the localization of tagged RFID objects. Regardless of the presence or ancillary information recognition of labelled objects with RFID Tags, there are many applications in which it would be useful to integrate said information with a possibly accurate estimate of the position of said objects in the physical world. Over time, various solutions have been proposed to identify the position of an object provided with RFID Tag, some of which are based on the use of arrays of antennas (for example in US2011032101 or in US20010035815) rather than an array of Tags in which the object acts as a shielding element (as in US2004113787). Recently, multi-antenna solutions with multiplexing have been proposed (as in patent application US20140197991), or hybrid solutions, based on the co-utilization of magnetic sensors and RFID identification systems, such as (US20130328825 or US20110181289), as well as solutions that use the Tags as waypoint to identify the position of vehicles in a railway (as in EP2765468A2) or in a work area (as in US20100141483).